Mat Foundation Settlement

Use of a larger foundation to produce lower soil contact pressures.

Mat foundation settlement.

Mat foundations are commonly used where settlements may be a problem for example where a site contains erratic deposits or lenses of compressible materials suspended boulders etc. Mat foundations are popular in areas where basements are common. Thus an allowable maximum settlement of 50 mm is usually specified for raft foundations. Common types of mat foundation.

Mat foundation is specified to bridge over pockets of weak spots in moderately weak soil. The mat foundation can be analysed as either rigid or flexible depending on the size and thickness of the mat and the strength of the subgrade. It has been found that for the same loading intensity and soil condition the differential settlement in a mat foundation is about 1 2 than that of a spread foundation. It is used to reduce differential settlement of buildings.

It is common to use mat foundation or deep basements to transfer the column loads to the underlying soil as well as provide floor slab for the basement. The designer can analyse a mat foundation of any size including up to 32 columns placed anywhere on the foundation. This spreadsheet can be used to complete the design of mat foundations. Raft or mat foundation is used when the soil layer is unstable.

Mat foundations are sometimes preferred for soils that have low load bearing capacities but that will have to support high column or wall loads. Mat foundation is also known as the raft foundation. The settlement tends to be controlled via the following. A mat foundation is used when the subsoil is weak and column loads are so heavy that the conventional spread footings cover more than 50 of the building area.

Under some conditions spread footings would have to cover more than half the building area and mat foundations might be more economical. Compared to spread footings the differential settlement in a mat foundation is much more reduced as the mat bridges over the loose pockets and lenses of a soil deposit. It is a continuous thick concrete slab on the soil that extends the entire footprint of the building and increases the soil bearing capacity power. The columns can be subjected to axial horizontal and moment forces.

If settlements beneath the mat foundation are more than the rigidity of the structure will permit a redistribution of loads takes place that will. The settlement of the mat foundation will be within limits that the structure can safely tolerate as a flexible structure.